The present invention relates to a tubing connector suitable for use with coiled tubing in oil and gas well operations.
Coiled tubing is primarily used to perform maintenance tasks on completed oil and gas wells. The principle of coiled tubing maintenance or xe2x80x98workoverxe2x80x99 is to attach a toolstring to the end of a reel of steel tubing. By reeling out the tubing, the toolstring may be lowered many thousands of feet into the well. By either reeling in or reeling out the tubing, the toolstring can be positioned and made to perform simple tasks downhole. The toolstring is retrieved by reeling in the tubing at the end of the task. Because the tubing is moderately rigid, in the same manner as drain rods, it is able to transmit torque and compression. This allows light drilling work and access to deviated sections where gravity alone would not be enough to convey the toolstring. Because coiled tubing is hollow, it is able to pass fluids. This feature may be used to place chemicals accurately at a given depth in the well. It may also be used to provide hydraulic power to the toolstring. The hydraulic power is typically used to activate tools and run hydraulic motors for example when drilling.
The tool string consists of a variable combination of individual tools screwed or otherwise locked together to form a working unit. A typical toolstring would comprise a tubing connector, non-return valves, accelerator, stem, upstroke jar and a running/pulling tool or motor and bit. The tubing connector joins the toolstring to the coiled tubing. Non-return or check valves are needed since the tubing passes through the wellhead seals. If the tubing broke at surface the non-return valves in the toolstring would shut and prevent escape of the well fluids. An accelerator stores energy in a spring system for use when hammering or xe2x80x98jarringxe2x80x99. The stem is lengths of dense tubing, the mass of which increases the momentum of the hammer blow when jarring. The upstroke jar is a latching slide hammer arranged so that the slide is latched closed until sufficient tension is applied to the toolstring via the tubing. The applied tension also compresses the springs in the accelerator, storing a measure of energy. When the jar latch releases, the jar rod and attached stem are accelerated by the stored energy. At the end of the jar rod travel the rod and stem are suddenly stopped giving a powerful hammer action. Setting the toolstring down after activating the upstroke jar pushes the jar rod back to the start of its travel and resets the latch. At the end of the toolstring there may be a running/pulling tool. This interfaces with equipment to be left in or retrieved from the well. In many cases a shear pin will need to be fractured to activate the running/pulling tool, thus the requirement for a hydraulically effect from the jar. Even if the running/pulling tool is hydraulically activated then, due to the arduous conditions of heat and contaminants downhole, mechanisms and interlocking parts can become jammed and require blows to free them. Alternatively, the coiled tubing tool string may end in a hydraulic motor and some form of drill bit or cutter. This equipment would be used for clearing obstructions or for deepening the well.
Another use for coiled tubing, especially in larger diameters, is as a permanent fixture in the well through which the oil or gas will be produced. This one-time deployment is often termed a hang-off. A coiled tubing hang-off is a fast and economical alternative to deploying screw-jointed tubulars. The tubing in the hang-off is suspended from and sealed to the existing well steelwork by a top connector. Typically the bottom tubing connector attaches filters, e.g. sand-screens or an electric submersible pump (ESP).
From the above descriptions it will be seen that the integrity of the connection between tubing and the tool string or hang-off components is of paramount importance. The tubing connector must be permanently secure when subject to large tensile, torque, shock and vibrational loadings. The connector must also allow a quick and foolproof assembly onto the tubing end as it hangs free from the tubing unit. Previous tubing connectors all present serious problems, either in security or assembly. These connectors may be divided into groups dependent upon their structure. Each group is described in turn below.
Grapple connectors, of which a typical example is shown in FIG. 1, use an externally tapered, internally serrated split sleeve to bite onto the coiled tubing and wedge into the connector body. The connector must be firmly assembled to the tubing before operations commence, this requiring large make up torques onto the free hanging tubing end. This is a difficult task. Large pull loads when in use will often cause the grapple to bite deeper onto the tubing and slip in its taper, so loosening the assembly thread which risks subsequent unscrewing and loss down hole. Since the grapple and tapered housing are outside the tubing this type of connector is xe2x80x98upsetxe2x80x99 or xe2x80x98outlinexe2x80x99 and the increased diameter of the assembly over the tubing diameter can pose an access problem in some wells. This connector is internally flush. The serrations inside the grapple 5 and the grapple location in the taper do not provide a good torque drive. When used for drilling this type of connector is normally enhanced with grub screws 3 through the connector body 1 top portion 4 biting into the tubing 2.
Pinned end connectors, of which a typical example is shown in FIG. 2, use a number of radial pins 6 loaded in shear to maintain a hollow spigot in the end of the tubing. The tubing is cross drilled to accept the pins using a guide jig and a pistol drill. The connector is assembled by placing the spigot in the tubing and pushing the pins through the tubing drilling and into matching blind holes in the spigot. An external sleeve 7 maintains the pins 6 in the connector. The connector transmits torque and tension commendably well but is tricky to assemble because of the predrilling required and the insertion of the small loose pins. The connector is neither internally nor externally flush.
Dimple grub screw connectors, a typical example of which is shown in FIG. 3, are also neither externally nor internally flush. Here the tubing end 2 is plastically worked by a jig so that it presents local depressions or dimples 8 into which grubscrews 3 in the connector 1 can seat. The connector itself is a sleeve which fits over the tubing and is threaded for the grubscrews. The connector has good tensile and torque capability.
Roll-on connectors, a typical example of which is shown in FIG. 4, are externally flush or xe2x80x98inlinexe2x80x99 connectors which use an internal spigot-type connector body 1. In this case the spigot is retained by plastically deforming or xe2x80x98crimpingxe2x80x99 the tubing into grooves 9 running around the spigot. The deformation is achieved with a manual pipe cutting tool in which the sharp cutting wheel is replaced by a radiused wheel to suit the grooves in the spigot. Some measure of torque transmission can be achieved by stopping one or more of the spigot grooves from being fully circumferential. This increases the difficulty of make up since the rolling tool cannot be run all the way round the tubing but must stop in accordance with the part grooves. The connector has limited tensile strength because of severe stress concentrations. Those, present around the full circumference of the tubing, are introduced by load transfer through the crimped profile.
It is an object of the present invention to overcome these disadvantages with a simple, remarkably robust, torque transmitting tubing connector of novel design that does not significantly diminish the tubing strength at the connection either in torque or in tension.
According to a first aspect of the present invention there is provided a tubing connector non-releasably connected to a tube of tubing string for use downhole in oil and gas well operations, the connector comprising an end portion fitted concentrically within or over a corresponding end of the tube, the end portion having a plurality of depressions coinciding with corresponding depressions on the corresponding end of the tube whereby the connector body and tube are connected together, the depressions in the tube having been formed by localised plastic deformation of the walls of the tube.
Preferably, the connector body is machined with depressions or through-holes receiving the plastically deformed tube therein. The very great benefit of this arrangement is that it is not restricted to only the very most pliable tubing materials and thicknesses and connector body materials and thicknesses since the plastic dimple-forming process is applied only to the interior or exterior of the tubing and does not need to simultaneously plastically deform the connector body. The resulting connector strengths in torsion and tension are accordingly much greater.
Preferably the local depressions in the tubing are circular through having been formed by an approximately spherical or conical shape impinging on the tube as from a hard ball or cone.
Preferably the connector body is formed having a male/spigot portion inserted into the corresponding end of the tubing.
In this last described arrangement the tubing is suitably locally depressed into mating engagement with the connector body by mounting a jig over the tubing having dimple-forming screws or pins mounted thereon.
The jig is preferably formed as a sleeve and is preferably formed in segments that are hinged together to clamp around the tubing during use of the jig.
The jig suitably has an annular recess extending around each end thereof to enable mounting of a yoke thereto, which yoke has a pneumatic or hydraulic ram to press the dimple-forming screw/pin(s) of the jig into the tubing.
Preferably, where the jig has the aforementioned recesses, those recesses have flat portions spaced around the circumference of the respective recess such that when the yoke is fully engaged the yoke is held both longitudinally of the jig and radially thereof but so that when the jaws of the yoke are only partially relieved the yoke may be radially reoriented around the jig but not moved longitudinally thereof.
According to a second aspect of the present invention there is provided a jig as defined in the preceding statements. According to a third aspect there is provided a yoke as defined in the preceding statements.
Further preferred features of the connector of the invention include that the coincident depressions of the tubing and connector body or coincident depression and hole are formed at more than one stage along the length of the connector body longitudinally of the tubing and, furthermore, that such depressions are provided at radially spaced intervals around the connector body and that the depressions are longitudinally staggered so that no two next radially adjacent depressions are located at the same position along the length of the connector body. This helps to minimise any concentration of points of weakening.
In the present invention where the connector body inserts within the tubing and is inter engaged therewith by action of an externally mounted jig collar it is easier to implement than using the converse arrangement having a jig inserted within the tubing to press the tubing out into the connector body. It avoids the need to insert a jig all the way down the very considerable length of the tubing with attendant difficulties of ensuring proper registration.
Where an internal jig is necessitated, this suitably comprises an elongate jig body having a plurality of balls arranged radially therearound and at longitudinal intervals therealong and which are pressed out into engagement with the tubing by a plurality of longitudinally spaced cam surfaces on the jig.